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Abstract

The biogeochemical characterization of marine particles suspended in sea water, is of fundamental importance in many areas of ocean science. Previous studies based on theoretical calculations and field measurements have demonstrated the importance of the use of the polarized light field in the retrieval of the suspended marine particles properties. However, because of the weakness of the water leaving polarized signal and of the limited number of appropriate spatial sensors, such measurements have never been exploited from space. Here we show that the marine polarized remote sensing reflectance, as detected from the POLarization and Directionality of the Earth’s Reflectances (POLDER) sensor, can be measured from space over bright waters and in absence of aerosols. This feasibility study is carried out over two oceanic areas characterized by different nature of the bulk particulate assemblage: the Barents sea during an intense coccolithophore bloom, and the Rio de la Plata estuary waters dominated by suspended sediments. The retrieved absolute values of the degree of polarization, P, its angular pattern, and its behavior with the scattering level are consistent with theory and field measurements. Radiative transfer simulations confirm the sensitivity of the POLDER-2 P values to the nature of the particulate assemblage. These preliminary results are very promising for the assessment of the bulk particle composition from remote sensing of the polarized signal, at least over highly scattering waters.

M. Chami, “Importance of the polarization in the retrieval of oceanic constituents from the remote sensing reflectance,” J. Geophys. Res. 112 (2007).
[Crossref]

M. Chami and M. Defoin-Platel, “Sensitivity of the retrieval of the inherent optical properties of marine particles in coastal waters to the directional variations and the polarization of the reflectance,” J. Geophys. Res.112, C05037, doi:10.1029/2006JC003758 (2007).
[Crossref]

M. Chami and M. Defoin-Platel, “Sensitivity of the retrieval of the inherent optical properties of marine particles in coastal waters to the directional variations and the polarization of the reflectance,” J. Geophys. Res.112, C05037, doi:10.1029/2006JC003758 (2007).
[Crossref]

Defoin-Platel, M.

M. Chami and M. Defoin-Platel, “Sensitivity of the retrieval of the inherent optical properties of marine particles in coastal waters to the directional variations and the polarization of the reflectance,” J. Geophys. Res.112, C05037, doi:10.1029/2006JC003758 (2007).
[Crossref]

M. Chami and M. Defoin-Platel, “Sensitivity of the retrieval of the inherent optical properties of marine particles in coastal waters to the directional variations and the polarization of the reflectance,” J. Geophys. Res.112, C05037, doi:10.1029/2006JC003758 (2007).
[Crossref]

Figures (6)

Degree of polarization P (in %) as a function of the scattering angle, θ, for two extreme refractive index relative to waters, n, and for two different values of the PSD slope, ζ: a) ζ=3, and b) ζ=4. c) Contour diagrams of P(90) as a function of the parameters n (x-axis), and ζ (y-axis). Note that the P values presented in this figure are not affected by multiple scattering in contrast to what happens in the ocean.

POLDER2 selected scenes of RGB composites, over (a) the Rio de la Plata estuary (26 of May 2003), and (b) off Norway in the Barents sea (19 of July 2003). The red line in panel a corresponds to a transect specifically examined, and the numbers represent the pixel number (see text for details).

Scatter plot of Rrs as a function of P at 670 nm for (a) the Rio de la Plata estuary, and (b) the Barents Sea areas. The black lines in panel a and b correspond to the fits described by the equations 2 and 3, respectively. The square correlation coefficient (r2) is given. Note the different scales of the two panels.

Variation of Rrs as a function of P for the value of the scattering angle of (a) 120° and (b) 130° for the Rio de la Plata estuary waters. The colored symbols represent data obtained from the radiative transfer simulations performed for different values of the refractive index, n, and PSD slope, ζ, as indicated. The black dots represent the data obtained from POLDER-2 observations. Note that the P values are lower than those presented in Fig. 1 for which the calculations did not account to multiple scattering.